The present invention relates to hydraulic accumulators, and more specifically, to fluid level indicators useful in determining the linear displacement of a piston within the accumulator.
Hydraulic accumulators are energy storage devices, typically used in many aircraft hydraulic systems. They usually employ stored gas as the variable energy source. Their applications include hydraulic pump ripple attenuation, momentary system power over-demand conditions, and performance of emergency actuation functions such as deploying a ram air turbine via a hydromechanical actuator.
The work output is dependent on initial precharge pressure, precharge temperature and delta volume change caused by piston movement under varying demand conditions. In order to monitor accumulator precharge condition, the charging pressure, temperature, and piston displacement must, therefore, be determined.
Prior art methods of determining fluid level displacement or piston displacement within a pressurized accumulator include electro-optical devices and direct action devices. Further details of an improved electro-optical system of this general type can be observed by a reading of U.S. Pat. No. 3,995,168, assigned to the common assignee herewith entitled Electro-Optical Fluid Measurement System, issued Nov. 30, 1976.
In one construction of a direct action accumulator device, a rod is attached to the piston which passes through a dynamic seal in the accumulator. In another construction, a rotary measuring device is attached to the piston on the oil side of the accumulator. Typically a linear potentiometer is connected to the movable piston rod such that a direct relationship can be obtained by measuring resistance versus displacement.
Accordingly, it is a principle object of the present invention to provide an accumulator fluid indicator wherein the linear displacement of a piston may be determined by sensor means mounted external to the pressurized fluid environment.
It is another object of the present invention to provide means for determining piston linear displacement without requiring the use of a dynamic seal.
It is a further object of the present invention to provide means for determining piston linear displacement wherein temperature compensation means eliminate output variations as a function of ambient temperature.